1. Field of the Invention
This invention relates to a receiving device and a receiving method.
2. Description of the Related Art
It is known that reception performance in mobile and other communications that are susceptible to fading, a phenomenon in which the received signal varies greatly over time, can be improved by a diversity scheme in which signals received from multiple antennas are combined. This technique improves reception performance by combining received signals including independent noise to reduce the noise effect.
There is a maximal ratio combining (MRC) method of obtaining a diversity combination output c in a receiving device having N antennas (where N is a natural number equal to or greater than 2) in which, as indicated in equation (1) below, the distortions experienced by the N received signals on their respective channels are estimated, the power values (p1 to pN) of the channel estimation results are normalized, and the received signals (d1 to dN) are weighted by the normalized values and then summed.
                    c        =                              ∑                          i              =              1                        N                    ⁢                                          ⁢                                    k              i                        ⁢                                          d                i                            ⁢                                                          (                                                k                  i                                =                                                      p                    i                                    /                                                            ∑                                              j                        =                        1                                            N                                        ⁢                                                                                  ⁢                                          p                      j                                                                                  )                                                          (        1        )            
Reception performance can be further improved by weighting the signals d1-dN with the normalized products of the power values p1-pN resulting from channel estimation and values (w1 to wN) resulting from signal quality estimation as in the following equation (2)
                    c        =                              ∑                          i              =              1                        N                    ⁢                                          ⁢                                    l              i                        ⁢                                          d                i                            ⁢                                                          (                                                l                  i                                =                                                      p                    i                                    ⁢                                                            w                      i                                        /                                                                  ∑                                                  j                          =                          1                                                N                                            ⁢                                                                                          ⁢                                                                        p                          j                                                ⁢                                                  w                          j                                                                                                                                )                                                          (        2        )            
A receiver described in Japanese Patent Application Publication No. 2003-110521 uses the carrier to noise (C/N) ratio obtained from the known signal estimation result as the result of signal quality estimation and perform diversity combination in a receiver with a plurality of antennas as in equation (2), estimating the C/N ratios from the squares of the distances of the results of known signal equalization to the closest ideal signal points.